1. Field of the Invention
The invention generally relates to permanent-split capacitor (PSC) motors and, in particular, to a reversible 4-pole/6-pole motor having a common winding in both the 4-pole configuration and the 6-pole configuration and having an additional winding in the 4-pole configuration only.
2. Description of the Prior Art
PSC motors, as one kind of single-phase induction motors, come in various multiple configurations and various pole configurations. For example, PSC motors are frequently used to drive washing machines for clothing. In particular, a 4-pole PSC has been used in vertical axis impeller washers. xe2x80x9cHowever, such impeller washers do not have a lower speed for a delicate washing cycle. In order to provide a variable speed motor which can operate at a slower speed for a delicate washing cycle, some configurations have used brushless permanent magnet motors, switched reluctance motors, or three-phase induction motors in combination with an electronic controller in place of the PSC motors.xe2x80x9d However, these configurations are expensive to produce.
One solution to this problem is described in co-invented, co-assigned U.S. Pat. No. 5,825,111 for SINGLE-PHASE INDUCTION MOTOR 4/6 POLE COMMON WINDING CONNECTION WITH MAGNETIC MOTIVE FORCE SYMMETRICALLY DISTRIBUTED, the entire disclosure of which is incorporated herein in its entirety. In this patent, a 4/6 pole PSC motor is described that provides a full shared winding and symmetrically distributed magnetic motive forces (MMF) for the 4-pole and 6-pole configurations. However, this motor has an air-gap flux density in the 4-pole configuration, which is about 18% higher than the air-gap flux density in the 6-pole configuration. In addition, the 4-pole forward and backward configurations have different break down torques (BDT) because of the higher resistance in the main winding energized in backward operation as compared to the resistance in the main winding energized in forward operation.
With increasing demand for impeller washers to have lower cost and higher performance, there is a need for a PSC motor which can operate at higher speeds to drive a regular washing cycle and which can also operate at lower speeds to drive a delicate washing cycle. In particular, there is a need for a reversible two-speed PSC motor having a high-speed configuration and having a low-speed configuration in which the air-gap flux density of both speed configurations can each be varied substantially independent of each other. There is also a need for a reversible two-speed PSC motor generating magnetic motive forces, which are symmetrically distributed about an air-gap between a rotor and a stator of the motor in both speeds.
To provide independently adjustable air-gap flux density in both speeds, the invention employs a new winding configuration. In this new configuration, the 4-pole configuration has an additional winding which is not energized in the 6-pole configuration. Both the 4-pole and 6-pole configurations achieve very good performance with this configuration. The additional winding has no effect on operation in the 6-pole configuration and reduces the saturation level for operation in the 4-pole configuration so that forward operation in the 4-pole configuration has a desirable saturation level independent of the 6-pole configuration. In the motor described in U.S. Pat. No. 5,825,111, the backward operation in the 4-pole configuration has a substantially lower saturation and break down torque (BDT) than forward operation in the 4-pole configuration because of the smaller wire size and higher resistance in the main winding. In the motor of the invention, the BDT during the backward operation in the 4-pole configuration is substantially increased because of the increased turns in the auxiliary winding.
It is an object of this invention to provide a 4-pole/6-pole PSC motor having a common main winding in both the 4-pole configuration and the 6-pole configuration and having an additional winding in the 4-pole configuration only; to provide such a motor which has efficient operation at two different speeds; and to provide such a motor which can be manufactured without significant re-tooling or redesign.
In one form, the invention is a 4/6 pole PSC motor having main and auxiliary winding configurations and having common windings energized in both a 4-pole configuration and energized in a 6-pole configuration for both the main and the auxiliary winding configurations. An additional winding is energized in the 4-pole configuration only. As a result, the air-gap flux level of the 4-pole configuration can be varied substantially independent of the air-gap flux level of the 6-pole configuration by varying the configuration of the additional winding.
In another form, the invention is a motor comprising a stator core, a rotor mounted in rotational relationship with the stator core, a plurality of windings components wound on the stator core, and an additional winding component wound on the stator core. The winding components are configured to be selectively energized to operate the motor in a 4N-pole configuration (N being an integer equal to or greater than one) in which the plurality of winding components and the additional winding component are energized. The winding components are configured to be selectively energized to operate the motor in a 6N-pole configuration in which the plurality of winding components only are energized. The additional winding component is not energized in the 6N-pole configuration and the additional winding component is energized only in the 4N-pole configuration.
In yet another form, the invention is an electric motor system comprising a pair of line terminals for connection to an external source of power, a stator core, a first winding coil group including four coil sets disposed in magnetic coupling relationship with the core, a second winding coil group including four coil sets disposed in magnetic coupling relationship to the core, a third winding coil group including four coil sets disposed in magnetic coupling relationship with the core, an additional winding coil including additional coil sets disposed in magnetic coupling relationship with the core and a switch assembly. The switch assembly is operatively connected to the first, the second, and the third winding coil groups and to the additional winding coil so as to change current flow direction in selected ones of the coil sets to provide a 4-pole configuration in one connection in which the additional winding coil is energized, and a 6-pole configuration in another connection in which the additional winding coil is not energized.
Other objects and features will be in part apparent and in part pointed out hereinafter.